You are looking for "backer rod". Here is an example:
http://www.bayindustries.com/backerrod/denverfoam.html
you need to install the appropriate size for the gap(s) you have.

Follow with the proper caulk/sealant like
There are several good manufacturers but these come to mind:
Vulkem
NP1, if the joints are fairly level use SL1 (self leveling)
DowCorning 795 silicone.

You can also fill the joints with pourable rubber sealant like:
http://www.apoc.com/Blackjack/bj-6435.htm or
http://www.wrmeadows.com/video/3405.wmv


(top posted for your convenience)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Keep the whole world singing . . . .
DanG (remove the sevens)




"peter" wrote in message
news:mDyvf.1922$ya.552@trnddc04...
There is a strip of rotting wood between the concrete slabs on
my driveway. It is about 1" wide. Is this a standard lumber
item, or would I have to cut it from something else? Is there
anything better than a strip of wood?

Between the driveway and walkway, and between the walkway slabs,
there are half-inch gaps but no wood strips in them. I don't
know what is supposed to be in these gaps, but now they are
filled with random junk/dirt and topped with moss. What is the
proper way to stuff these gaps?